The present invention relates generally to the field of computers and computer systems. More particularly, the present invention relates to a gate enhanced tri-channel positive charge pump.
Many of today""s computing applications such as cellular phones, digital cameras, and personal computers, use nonvolatile memories to store data or code. Nonvolatility is advantageous because it allows the computing system to retain its data and code even when power is removed from the computing system. Thus if the system is turned off or if there is a power failure, there is no loss of code or data.
One example of a nonvolatile memory device is the flash Electrically Erasable Programmable Read-only Memory (flash EEPROM or flash memory). Flash memory can be programmed by the user, and once programmed, the flash memory retains its data until the memory is erased. Electrical erasure of the flash memory erases the contents of the memory of the device in one relatively rapid operation. The flash memory may then be programmed with new code or data.
Flash memories have been used in portable computers and similar circuitry as both read only memory and as long term storage which may be both read and written. However, the tendency has been to reduce the power requirements of such portable computers to make systems lighter and to increase the length of use between recharging. This has required that the voltage potentials available to program the flash memory arrays be reduced. Flash memories must be able to operate in systems where a VCC supply voltage of 5V, 3V, or an even smaller voltage is available to circuit components. However, performing program and erase operations in flash memory components requires that greater voltage than that supplied to the component be applied to the flash memory cells. For example, a program operation may require that approximately 10.5V be applied to a memory cell. In order to achieve this voltage, a charge pump circuit is required in the flash memory component. A positive charge pump can take a supplied VCC voltage and create a voltage sufficient for program operations. The charge pump must also be able to deliver sufficient current at the required voltage levels.
As lower supply voltages are used with integrated circuit components, semiconductor processing technology has continued to improved. Along with these developments are transistor devices with lower threshold voltages (Vt). However, these lower Vt levels can cause problems when the Vt is small relative to the VCC supply voltage. As a result, devices may accidentally turn on or leak charge at undesired times.